The invention is directed to a method for producing polycrystalline layers having a granular crystalline structure as used for thin-film semiconductor components, particularly for silicon crystal cells. The polycrystalline layer is deposited from a gaseous, or vapor, phase onto insulating or electrically conductive substrates, or onto substrates having a coating of electrically conductive material, and through a subsequent heat treatment the layer is recrystallized.
Economic considerations have created a need to reduce the costs of solar cells and therefore, a need for new and more economic methods for the production of thin semiconductor layers. Previous methods for producing thin semiconductor layers, such as, for example, the epitaxial growth method for producing single-crystalline layers on suitable substrates, are too expensive to be used for creating solar cells and are therefore not utilized; even though they create the highest quality thin semiconductor layers. Examples of methods for manufacturing solar cells are set forth in, for example, the periodical VDI-Z-121 (1979), No. 8, April, pages 389 through 393.
When the layer are to be utilized in applications wherein defects in the crystalline, active semiconductor layer can be tolerated, with reference to the efficiency of the device, such as, for example, in solar cells, lower cost substrates are desireable as carriers for the thin layers produced thereon. To this end, for example, sheet metal can be used for this purpose. The layers can be deposited on these substrates from the vapor phase. Methods that proceed at lower temperatures are preferable. This, on the one hand, accommodates the selection of the material for the substrates, and also lowers the cost of the method by lowering the expenditure of energy.
The layers that are created, however, have the disadvantage that they contain an excessively great number of grain boundaries. The grain diameters typically are below 1 .mu.m. It is possible, however, to recrystallize these layers in order to improve the quality. To this end, for example, heated graphite rods can be passed over the layer, near the surface of the layer. The layer can also be superficially recrystallized with a suitable lamp and optics. High surface speeds can be achieved. But, the influence of the crystalline substrate creates some problems; the crystal structure thereof can have an unfavorable influence on the process of recrystallization, or the recrystallization can be prevented since the microcrystallites of the substrate always influence the thin films situated thereon.